This application is a 35 USC 371 application of PCT/DE 00/01726 filed on May 27, 2000.
1. Field of the Invention
The invention is based on an apparatus for rapid pressure buildup in a motor vehicle device supplied with a pressure medium by a feed pump, in particular in a reservoir-type injection system (common rail) supplied with pressure by a high-pressure pump.
2. Description of the Prior Art
In modern internal combustion engines, high-pressure injection systems are increasingly used in which fuel is kept on hand in a storage volume at high pressure, so as to be distributed to injection valves, an example being reservoir-type injection systems (common rails) in self-igniting internal combustion engines and direction injection systems in internal combustion engines with externally supplied injection. In such high-pressure injection systems, the problem arises that even during starting of the engine, an adequately high pressure must be built up in the injection system. As a rule, the high-pressure fuel pumps used to supply the high-pressure injection systems with fuel are driven by the engine crankshaft, so that the pressure buildup at starter rpm proceeds too slowly and lengthens the starting time. Thus not only the high-pressure fuel pumps but also prefeed pumps are used, so that an adequate pressure level can be made available for starting. However, this means an increase of pollutants in the exhaust.
Furthermore, electrohydraulic valve control devices for gas exchange valves of internal combustion engines also operate at high pressure, at which hydraulic oil is brought by a hydraulic pump to a pressure level of 100 bar, for instance, for actuating gas exchange valve actuators hydraulically. Once again, the problem arises that the high pressure must already be available upon starting of the engine.
From European Patent Disclosure EP 0 455 761 B1, a hydraulic valve control device for controlling the gas exchange valves of an internal combustion engine is known, with a control pressure reservoir disposed upstream of a magnet valve and containing a piston, which defines a pressure chamber that can be increased in size counter to the force of a spring element prestressed counter to the piston. The pressure chamber of the control pressure reservoir is connected to a feed pump of the valve control device and can be made to communicate with its control lines via the magnet valve. While the magnet valve is in the closing position, the piston, because of the pressure built up in the pressure chamber by the feed pump, is forced, counter to the action of the spring element, into a position that increases the size of the pressure chamber. When the magnet valve is open, the pressure in the pressure chamber drops, because some of the hydraulic oil flows into the control lines. Because of the dropping counter pressure, the piston can decrease the size of the pressure chamber because of its spring prestressing, resulting in a pressure surge that makes it possible to make the control pressure in the control lines still more precise and to maintain that pressure.
In order beyond this originally provided purpose to make it possible also to keep high pressure available for an ensuing restart after the engine has been put out of operation, the magnet valve would have to remain closed during the entire time that the engine is off, so as to keep the pressure chamber constantly at high pressure and to keep the piston prestressed. Proceeding in this way, however, entails the problem that even the slightest leakages would mean that the high pressure in the pressure chamber would be degraded over time, and thus not enough pressure would be available for the restart of the engine. Furthermore, safety concerns advise against keeping high pressure on hand in a pressure reservoir of a motor vehicle, because if improper work is done on the pressure reservoir, accidents can happen.
The apparatus according to the invention has the advantage over the prior art that the piston used to generate a rapid pressure rise can be kept in its energy-storing position, prestressed counter to the spring element, solely by the locking device according to the invention. Thus leaks in the line system that cause a pressure loss in the pressure chamber cannot also lead to a loss of the energy stored by the piston. Since when the engine is off, because the feed pump is not in operation then, the pressure chamber is virtually without pressure anyway, if work is done on the motor vehicle there is no risk that the high pressure stored in the pressure chamber will discharge by itself.
In a preferred embodiment of the invention provides that the piston is guided longitudinally displaceably inside a closed cylinder, and the pressure chamber is formed between the piston and a bottom of the cylinder; this bottom is provided with a pressure connection, and by way of this bottom the pressure chamber is connected to a pressure line that effects communication between the feed pump and the device.
Expediently, the locking device includes two locking bolts, received in diametrically opposed receiving bores in the cylinder wall and in the outset position protruding into the cylinder in a direction transverse to the direction of motion of the piston and preferably prestressed in this direction by helical springs, which bolts can be forced back into their receiving bores by the motion of the piston in the direction of its locking position and, after the piston has moved past the bolts and reached its locking position, the bolts positively engage at least the edge of the piston, emerging from their receiving bores.
By the provisions recited, an automatic locking of the piston is attained because the pressure existing in the system assures that the piston will move past the locking bolts and push them back into their receiving bores. Once the piston has then reached its locking position, the spring-prestressed locking bolts automatically move out of the receiving bores and lock the piston.